LA-ICP-MS zircon U-Pb ages and petrogenesis of granodiorite in Mengguyingzi, Chifeng, Inner Mongolia

Located in the south of the Xing'an-Mongolian orogenic belt in northern North China plate, the Mengguyingzi granites are mainly composed of granodiorite. All samples show chemical signatures of high-K calc-alkaline I-type granites and have the following characteristics: SiO2 is about 56.88%~68.82%, Na2O is about 4.32%~4.54%, K2O is about 2.3%~3.86%, Na2O>K2O, Rittmann index σ=2.08~2.33, Al2O3 is about 15.1%~16.8%, and A/CNK=0.81~0.92. The granodiorite is enriched in light rare earth (LREE) and relatively depleted in heavy rare earth (HREE) and high field strength elements. The content of Sr is about 782×10-6~1230×10-6, and the average values of Y and Yb are 20.1×10-6 and 1.77×10-6 respectively. δEu=0.81~1.04, and Eu anomaly is not obvious. The granodiorite shows C adakitic rock geochemical properties, implying that its magma might have been derived from partial melting of the thickened lower continental crust. The zircon 206Pb/238U age of granodiorite measured by LA-ICP-MS zircon U-Pb dating is 252.8±2.4Ma, implying that the Mengguyingzi granodiorite were formed in the late Paleozoic-Early Mesozoic. Combined with the tectonic evolution of the Xing'an-Mongolian orogenic belt, the authors hold that the Mengguyingzi granodiorite resulted from post-collision between Siberia plate and North China plate and suggested that the underplating of mantle-derived magma induced crustal growth.